GBC_004_E1_0 Radio Parameters Course Objectives: Contents

GBC_004_E1_0 Radio Parameters

Course Objectives:

Understand the meanings of various

radio parameters

Master the impact of the settings of

radio parameters on radio network

performance

Contents

1 Network Identity Parameters.........................................1

1.1 Cell Global Identity (CGI).....................................1

1.1.1 Definition................................................1

1.1.2 Format....................................................1

1.1.3 Setting and Influence.....................................2

1.1.4 Precautions...............................................3

1.2 Base Station Identity Code (BSIC)..............................3

1.2.1 Definition................................................3

1.2.2 Format....................................................5


1.2.4 Precautions...............................................6

2 System Control Parameters...........................................7

2.1 BCCH Carrier Transmitted Power (BSPWRB)........................7

2.1.1 Definition................................................7

2.1.2 Format....................................................7


2.2 Common Control Channel Configuration (CCCH_CONF)...............7

2.2.1 Definition................................................7

2.2.2 Format....................................................8


2.3 Access Grant Blocks (AGBLK)....................................8

2.3.1 Definition................................................8

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2.3.2 Format....................................................9


2.4 Paging Channel Multiframes (BS-PA-MFRMS)......................10

2.4.1 Definition...............................................10

2.4.2 Format...................................................10

2.4.3 Setting and Influence....................................11

2.4.4 Precautions..............................................12

2.5 Radio Link Timeout (RLT)......................................12

2.5.1 Definition...............................................12

2.5.2 Format...................................................12


2.5.4 Precautions..............................................13

2.6 Network Color Code Permitted (NCCPERM)........................13

2.6.1 Definition...............................................13

2.6.2 Format...................................................14


2.6.4 Precautions..............................................14

2.7 Cell Bar Access (CBA).........................................14

2.7.1 Definition...............................................14

2.7.2 Format...................................................14


2.7.4 Precautions..............................................15

2.8 Cell Bar Qualify (CBQ)........................................15

2.8.1 Definition...............................................15

2.8.2 Format...................................................15


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2.8.4 Precautions..............................................16

2.9 Access Control Level (AC).....................................16

2.9.1 Definition...............................................16

2.9.2 Format...................................................17


2.9.4 Precautions..............................................18

2.10 MAX RETRANS..................................................18

2.10.1 Definition..............................................18

2.10.2 Format..................................................18

2.10.3 Setting and Influence...................................19

2.11 Transmission Distribution Timeslots (Tx_integer).............19

2.11.1 Definition..............................................19

2.11.2 Format..................................................20


2.12 IMSI Attach/Detach Permission (ATT)..........................21

2.12.1 Definition..............................................21

2.12.2 Format..................................................22


2.12.4 Precautions.............................................22

2.13 Periodical Location Update Timer (T3212).....................23

2.13.1 Definition..............................................23

2.13.2 Format..................................................23


2.13.4 Precautions.............................................24

2.14 Multi-band Indication (MBCR).................................24

2.14.1 Definition..............................................24

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2.14.2 Format..................................................24


2.15 CLASSMARK Early Sending Control (ECSC).......................25

2.15.1 Definition..............................................25

2.15.2 Format..................................................26


2.15.4 Precautions.............................................26

2.16 Wait Indication T3122........................................27

2.16.1 Definition..............................................27

2.16.2 Format..................................................27


2.16.4 Precautions.............................................27

3 Cell Selection Parameter...........................................29

3.1 RXLEV_ACCESS_MIN..............................................29

3.1.1 Definition...............................................29

3.1.2 Format...................................................30


3.1.4 Precautions..............................................30

3.2 Cell Selection Hysteresis.....................................31

3.2.1 Definition...............................................31

3.2.2 Format...................................................31


3.2.4 Precautions..............................................32

3.3 Cell Reselection Offset (CRO), Temporary Offset (TO) and PenaltyTime (PT).........................................................32

3.3.1 Definition...............................................32

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3.3.2 Format...................................................34

3.3.3 Precautions..............................................34

3.4 MS_TXPWR_MAX_CCH..............................................34

3.4.1 Definition...............................................34

3.4.2 Format...................................................35


3.5 Cell Reselection Parameter Indication (PI)....................36

3.5.1 Definition...............................................36

3.5.2 Format...................................................36


3.6 Additional Reselection Parameter Indication (ACS).............36

3.6.1 Definition...............................................36

3.6.2 Format...................................................36


4 Network Function Parameters........................................37

4.1 MS Dynamic Power Control Status...............................37

4.1.1 Definition...............................................37

4.1.2 Format...................................................37


4.2 Frequency Hopping Status (H)..................................37

4.2.1 Definition...............................................37

4.2.2 Format...................................................37


4.3 Hopping Sequence Number (HSN).................................38

4.3.1 Definition...............................................38

4.3.2 Format...................................................38

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4.4 Mobile Allocation Index Offset (MAIO).........................39

4.4.1 Definition...............................................39

4.4.2 Format...................................................39


4.5 Discontinuous Transmission (DTX)..............................39

4.5.1 Definition...............................................39

4.5.2 Format...................................................39


4.6 Average Cycle of Idle Channel Interference Level (INTAVE).....40

4.6.1 Definition...............................................40

4.6.2 Format...................................................40


4.7 Interference Band Edge (LIMITn)...............................40

4.7.1 Definition...............................................40

4.7.2 Format...................................................40


4.7.4 Precautions..............................................41

4.8 New Cause Indication (NECI)...................................41

4.8.1 Definition...............................................41

4.8.2 Format...................................................42


4.9 Call Reestablishment Permission (RE)..........................42

4.9.1 Definition...............................................42

4.9.2 Format...................................................42


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1 Network Identity Parameters

1.1 Cell Global Identity (CGI)

1.1.1 Definition

As a global cellular mobile communication system, each GSMnetwork of every country or even each location area, BTSand cell in each network have strict numbers, to ensurethat every cell worldwide has a unique number. The use ofthis numbering scheme can achieve the following purposes:

It allows the MS to correctly identify the current networkso that it can select the network the subscriber (oroperator) wants to enter in any environment.

It allows the network to know the exact location of a MSin real time so that the network can normally connectvarious service requests to the MS.

It allows the MS to report the correct adjacent cells tothe network during calls, so that the network can maintainthe calls through handover when necessary.

The CGI is one of the major network identity parameters.

1.1.2 Format

Fig. 1.1 -1 shows the schematic diagram for the CGI.

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Fig. 1.1-1 Composition of the CGI

The CGI is composed of the Location Area Identity (LAI)and Cell Identity (CI). The LAI further includes MobileCounty Code (MCC), Mobile Network Code (MNC) and LocationArea Code (LAC), as shown in Fig. 1.1 -1. The CGIinformation is sent in the system messages broadcast byeach cell. When a MS receives the system messages, itextracts the CGI information inside and determine whetherit can camp on the cell according to the MCC and MNCindicated by the CGI. At the same time, it checks whetherthe current location area has changed to determine whetherlocation update is required. During the location updateprocess, the MS reports the LAI information to the networkto allow the network to know the exact cell where the MSis in. The format of the CGI is MCC-MNC-LAC-CI.

MCC: It consists of three decimal numbers, within therange of 000 ~ 999 (decimal). It is 460 for China.

MNC: It consists of two decimal numbers, within the rangeof 00 ~ 99 (decimal).

LAC: It is within the range of 1~65535. The LAC is 00 forChina Mobile, and 01 for China Unicom.

CI (Cell Identity): It is within the range of 0 ~ 65535.

1.1.3 Setting and Influence

As a global unique country identity standard, the MCCresources are allocated and managed by ITU in a unifiedmanner. The mobile country code for China is 460(decimal).

The MNC is usually allocated by the related telecommanagement authority of a country in a unified manner.Currently, there are two GSM networks in China, which arerun by China Telecom and China Unicom, with the MNCs to be

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2 System Control Parameters

00 and 01 respectively.

Each country has its specification for the coding methodof LAC. China Telecom has specification for the codingmethod of LAC on its GSM network without exception (Fordetails, see the related specification for GSM publishedby the former Ministry of Posts and Communications ofChina). Usually, in the earlier stage when a network isbuilt, the allocation and coding of the LAC are determinedand are seldom modified during running.

The size of LAC (that is, the coverage of one LAC) is avery key factor in the system. Generally, you should makethe location area as large as possible.

For the allocation of the CI, there is no specialrestriction, and it can be any value within 0~65535(decimal). However, you must ensure that not any two cellsin one location area have the same CI. Usually, this hasalready been determined in the system design of thenetwork. Unless in special cases (for example, BTSs areadded in the system), you should not modify the CI duringthe running of the system.

1.1.4 Precautions

The MCC should not be modified.

The MNC should not be modified.

The LAC should be set in strict accordance with therelated specification of China Telecom. Avoid the caseswhere two or more location areas in the network(throughout the country) have the same LAC.

When you set the CI, you must note that no two or morecells can have the same CI in one location area.

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1.2 Base Station Identity Code (BSIC)

1.2.1 Definition

In the GSM system, each BTS is allocated with one localcolor code, known as BSIC. If a MS can receive the BCCHcarriers of two cells at a location with the same channelnumber, the MS distinguishes them according to the BSIC.In network planning, the BCCH carriers of the adjacentcells should use different frequencies in order to reduceco-frequency interference. On the other hand, thecharacteristics of the cellular communication systemdetermine that the BCCH carriers are certain to have thepossibility of reuse. For these cells using the same BCCHcarrier frequencies, you must ensure that they havedifferent BSICs, as shown in Fig. 1.2 -2.

Fig. 1.2-2 Schematic Diagram for Selection of BSIC

In the diagram, the BCCH carriers of cells A, B, C, D, Eand F have the same absolute channel numbers, and othercells use different channel numbers as the BCCH carriers.Usually, cells A, B, C, D, E and F must use the same BSIC.When the BSIC resource is insufficient, different BSICsshould be first ensured for the close cells. For cell E,if there are not sufficient BSIC resources, differentBSICs should be first used for cells D and E, B and E, andF and E, while cells A and E, and C and E can have thesame BSICs.

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Its major functions are:

1. After a MS receives the SCH, it believes that it hasbeen synchronized with the cell. However, tocorrectly decode the information on the downlinkpublic signaling channel, the MS also needs to knowthe Training Sequence Code (TSC) used by thesignaling channel. According to the specification ofGSM, the TSC is available in eight fixed formats,which are represented with sequence numbers 0 ~ 7respectively. The common signaling channel of eachcell uses the TSC determined by the BCC of the cell.Therefore, one of the functions of the BSIC is tonotify the MS of the TSC used by the common signalingchannel of the current cell.

2. Since the BSIC has participated in the decodingprocess of the Random Access Channel (RACH), it canbe used to prevent the BTS from sending the MS to theRACH of the adjacent cell, for misinterpretation asthe access channel of the current cell.

3. When the MS is in the connection mode (during calls),it measures the BCCH carrier of the adjacent cell andreports the results to the BTS, according to thespecification of the adjacent cell table on the BCCH.At the same time, the MS must give the BSIC of thecarrier it has measured for each frequency point inthe uplink measurement report. When in a specialenvironment where the adjacent cells of one cell havetwo or more cells use the same BCCH carriers, the BTScan distinguish these cells based on the BSIC, toavoid incorrect handover, or even handover failure.

4. The MS must measure the signals of the adjacent cellsin the connection mode (conversation process), andreports the measurement results to the network. Since

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each measurement report sent by the MS only includesthe contents of six adjacent cells, the MS must becontrolled to report only the cells actually withhandover relationships with the current cells. Thehigher three bits in the BSIC (that is, NCC) are usedfor the above purpose. The network operator can usethe broadcast parameter “allowed NCC” to control theMS to report the adjacent cells with the NCCs in theallowed range.

1.2.2 Format

The BSIC consists of the Network Color Code (NCC) and BaseStation Color Code (BCC), as shown in Fig. 1.2 -3. TheBSIC is transmitted on the Synchronization Channel (SCH)of each cell.

Fig. 1.2-3 Composition of the BSIC

Format of the BSIC: NCC-BCC

Range of the NCC: 0 ~ 7

Range of the BCC: 0 ~ 7


In many cases, different GSMPLMNs use the same frequencyresources, which, however, are somewhat independent innetwork planning. To ensure that the adjacent BTSs withthe same frequency points have different BSICs in thiscase, it is usually specified that the adjacent GSMPLMNsshould select different NCCs.

It is special in China. Strictly speaking, the GSM network

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provided by China Telecom is a complete and independentGSM network. Although China Telecom has numerous localmobile offices under it, they all belong to one operator –China Telecom. However, as China is a large country with avast territory, it is very difficult to implement completeunified management. Therefore, the entire GSM network isdivided into parts managed by the mobile offices (or localorganizations) in various provinces and cities. On theother hand, the mobile offices in various places areindependent of each other in network planning. To ensurethat the BTSs with the same BCCH frequencies on theborders between various provinces and cities havedifferent BSICs, the NCCs of various provinces and citiesin China should be managed by China Telecom in a unifiedmanner.

As part of the BSIC, the BCC is used to identify differentBTSs with the same BCCH carrier number in one GSMPLMN. Itsvalue should meet the above requirement as far aspossible. In addition, according to the GSM specification,the TSC of the BCCH carrier in a cell should be the sameas the BCC of the cell. Usually, the manufacturer shouldmaintain such consistency.

1.2.4 Precautions

It must be ensured that the adjacent or nearby cells withthe same BCCH carrier have different BSICs. Particularly,when the adjacent set of one cell has two more cellshaving the same BCCH carriers, it must be ensured thatthese two cells have different BSICs. You must pay specialattention to the configuration of the cells on the bordersof various provinces and cities to avoid inter-cellhandover failure.

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2.1 BCCH Carrier Transmitted Power (BSPWRB)

2.1.1 Definition

The outputted power level of the BTS is usuallyadjustable, and different power levels can be set for BCCHcarriers and non-BCCH carriers. Power level means theoutputted power of the power amplifier. The BSPWRB setsthe transmitted power level of the BCCH carrier of theBTS. This parameter has a huge impact on the coveragerange of the BTS.

2.1.2 Format

The BSPWRB is a decimal number, in dBm, within the rangeof 0 ~ 46.

2.1.3 Setting and InfluenceThe BSPWRB has a huge impact on the actual coverage rangeof the cell. If this parameter is set to too high a level,the actual coverage range of the cell will become larger,causing great interference to the adjacent cells. If thisparameter is set to too small a value, gaps may occurbetween adjacent cells, causing “blind areas”. Therefore,the BSPWRB should be strictly based on the design ofnetwork planning. Once set, do not change them in runningunless absolutely necessary.

When the network is expanded or due to other reasons (forexample, the geographical environment changes), theparameter should be modified. Before and after theparameter is modified, you should perform complete field

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strength test on site, and adjust the coverage range ofthe cell according to the actually conditions.

2.2 Common Control Channel Configuration (CCCH_CONF)

2.2.1 DefinitionThe CCCH can be borne by one physical channel or multiplephysical channels, and the CCCH and the SDCCH can shareone physical channel. The combination mode of the CCCH ina cell is determined by the CCCH_CONF.

2.2.2 Format

The CCCH_CONF consists of three bits, as shown in Table 2.2 -1.

Table 2.2-1 CCCH_CONF Code and Meaning

CCCH_CONFCode

MeaningNumber of CCCH

Message Blocks inOne BCCH Frame

000CCCH uses one basic physicalchannel, not shared with theSDCCH

9

001CCCH uses one basic physicalchannel, shared with the SDCCH

3

010CCCH uses two basic physicalchannels, not shared with theSDCCH

18

100CCCH uses three basic physicalchannels, not shared with theSDCCH

27

110CCCH uses four basic physicalchannels, not shared with theSDCCH

36

Others Reserved

10



The configuration of the CCCH_CONF is determined by theoperator according to the traffic model of the cell,usually in the system design stage. According to thecommon experience, when the number of TRXs in the cell is1 or 2, the CCCH is recommended to use one physicalchannel shared with the SDCCH. When the number of TRXs inthe cell is 3 or 4, the CCCH is recommended to use onephysical channel not shared with the SDCCH. The case wherethe number of TRXs exceeds four needs further study.

2.3 Access Grant Blocks (AGBLK)

2.3.1 Definition

Since the CCCH consists of both the Access Grant Channel(AGCH) and Paging Channel (PCH), it must be set how manyblocks will be reserved for the AGCH in the CCCH channelmessage blocks on the network. To allow the MS to knowsuch configuration information, the system messages ofeach cell include one configuration parameter, that is,the Access Grant Blocks (AGBLK).

2.3.2 Format

The AGBLK means the blocks for the AGCH in the CCCH. Itsmeaning is shown in Table 2.3 -2.

Table 2.3-2 Table of the AGBLK

Combinationbetween BCCH and

SDCCHAGBLK Code

Number of Blocks Reserved forthe AGCH in Each BCCH Multi-

frame

Combined0 01 12 2

Not combined 0 0

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1 12 23 34 45 56 67 7


The AGBLK is a decimal number, in the following range:

When CCCH is not combined with SDCCH: 0 ~ 7

When CCCH is combined with SDCCH: 0 ~ 2

The default value is 1.

After the combination is determined between CCCH andSDCCH, the parameter AGBLK is actually the percentage forallocation between the AGCH and PCH in the CCCH. Thenetwork operators can balance the load between the AGCHand PCH by adjusting this parameter. You can observe thefollowing principles when you are doing this:

1. The AGBLK should take the following value: On theprecondition that the AGCH is not overloaded, theparameter should be kept as small as possible toshorten the time the MS responds to the paging, forhigher service performance.

2. Usually, the AGBLK should be 1 (CCCH and SDCCH arecombined), 2 or 3 (when CCCH and SDCCH are notcombined).

3. In the running network, you can appropriately adjustthe AGBLK in measuring the overload of the AGCH.

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2.4 Paging Channel Multiframes (BS-PA-MFRMS)

2.4.1 Definition

According to the GSM specification, every MS subscriber(corresponding to each IMSI) belongs to one paging group.For the calculation of the paging group, see GSM 05.02. Ineach cell, every paging group corresponds to one pagingsub-channel, and the MS calculates its paging groupaccording to its own IMSI, and further the location of thepaging sub-channel belonging to the paging group. In anactual network, a MS can only “listen to” its paging sub-channel while ignoring the contents on other sub-channels.When it is in other paging sub-channels, it even turns offthe power of some its hardware devices to save power (thatis, the source of the DRX). The BS-PA-MFRMS defines thenumber of multiframes forming a cycle of the paging sub-channel. In fact, the parameter determines how many pagingsub-channels a paging channels in a cell are allocated to.

2.4.2 Format

The BS-PA-MFRMS is a decimal number, and its meaning isshown in Table 2.4 -3.

Table 2.4-3 Meaning of the BS-PA-MFRMS

BS-PA-MFRMSNumber of Multi-frames Cycled on the Same Paging

Channel in the Same Paging Group2 23 34 45 56 67 78 89 9

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It is within the range of 2 ~ 9, in multi-frames (51frames), defaulted to 2.

According to the combination between CCCH and SDCCH, andthe definitions of the AGBLK and BS-PA-MFRMS, you cancalculate the number of paging sub-channels of each cell:

1. When CCCH and SDCCH are combined: (3-AGBLK) × BS-PA-MFRMS.

2. When CCCH and SDCCH are not combined: (9-AGBLK) × BS-PA-MFRMS.

According to the above analysis, the larger the BS-PA-MFRMS, the more the paging sub-channels of the cell, andaccordingly the lower the number of subscribers belongingto each paging sub-channel. For details, see thecalculation about the paging group in the GSM 05.02.Therefore, the bearer capability of the paging channelbecomes more powerful. Note that the capacity of thepaging channel has not increased in theory, but that thebuffer of the paging messages is expanded for each BTS,for evener transmission of paging messages in time andspace. However, the above advantage is obtained at thecost of the average delay of the paging message on theradio channel. In other words, the larger the BS-PA-MFRMSis, the greater of the delay of the paging messages in thespace segment becomes, and the average service performanceof the system decreases. Obviously, the BS-PA-MFRMS is animportant parameter for network optimization.

When network operators set the BS-PA-MFRMS, they arerecommended to observe the following principles:

1. The BS-PA-MFRMS should be selected according to theprinciple that the paging channels are not

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overloaded, and the parameter should be kept as smallas possible under this precondition.

2. The general recommendation is that you should set theBS-PA-MFRMS to 8 or 9 (that is, 8 or 9 multi-framesare used as the cycle of the paging group) for theareas where the paging channel is heavily loaded(usually the areas with heavy traffic). You shouldset the BS-PA-MFRMS to 6 or 7 (that is, 6 or 7 multi-frames are used as the cycle of the paging group) forthe areas where the paging channel is ordinarilyloaded (usually the areas with appropriate traffic).You should set the BS-PA-MFRMS to 4 or 5 (that is, 4or 5 multi-frames are used as the cycle of the paginggroup) for the areas where the paging channel islightly loaded (usually the areas with smalltraffic).

3. In the running network, the load of the pagingchannel should be measured at periodical intervals toprovide the data based on which the BS-PA-MFRMS canbe appropriately adjusted.

2.4.4 Precautions

Since any paging message in a location area (with the sameLAC) must be sent in all the cells in the location area,the paging channel capacity of each cell in the samelocation area should be the same or close to each other asfar as possible (meaning the number of paging sub-channelscalculated of each cell).

2.5 Radio Link Timeout (RLT)

2.5.1 Definition

When the downlink voice (or data) quality of the MS

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degrades to the unacceptable level during communicationand cannot be improved by RF power control or handover(that is, the so-called radio link failure), the MS willeither start call re-establishment or forcedly clear thelink. Since the forced link clearing actually introducesone “call drop” process, it must be ensured that the MSdeems a downlink radio link failure only when thecommunication quality really becomes unacceptable (usuallywhen the subscribers have to hang up the call). For thisreason, the GSM specification stipulates that the MS musthave a timer (S), which is assigned with an initial valueat the start of the conversation, that is, the “downlinkradio link timeout” value. Every time the MS fails todecode a correct SACCH message when it should receive theSACCH, the S is decreased by 1. On the contrary, everytime the MS receives a correct SACCH message, the S isincreased by 2, but the S should not exceed the downlinkradio link timeout value. When the S reaches 0, the MSwill report the downlink radio link failure.

2.5.2 Format

The radio link timeout is a decimal number, within therange of 4 ~ 64, at the step of 4, defaulted to 16.


The magnitude of the “downlink radio link timeout”parameter may affect the call interruption ratio andresource utilization of the network.

It is critical that the network operator should set thisparameter to an appropriate value. The setting of theparameter is closely related to the actual application ofthe system. Usually, you can observe the following rules:

1. In the areas with low traffic volume (usually remoteareas), the parameter should be set to 52 ~ 64.

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In the areas with low traffic volume while a largecoverage radius (suburbs or rural areas), this parametershould be set to 36 ~ 48.

In the areas with heavy traffic (usually cities), theparameter should be set to be 20 ~ 32.

In the areas with extremely heavy traffic (usually coveredby micro cells), the parameter should be set to 4 ~ 16.

For the cells with obvious blind areas or the areas withsevere call interruption during moving, the parametershould be increased appropriately.

2.5.4 Precautions

On the BTS side, there is also the means to monitor theradio link failure, but the monitoring method can be basedon the uplink SACCH error or on the uplink reception leveland reception signal quality. According to the GSMspecification, the radio link monitoring mode on the BTSside is determined by the carrier, and so is related tothe system the carrier has purchased. It should be notedthat the uplink/downlink monitoring standards must be onthe same level.

2.6 Network Color Code Permitted (NCCPERM)

2.6.1 Definition

In the connection mode (conversation process), the MSneeds to report to the BTS the signal strength of theadjacent cells it measures, but each report canaccommodate those of up to six adjacent cells only.Therefore, it must be ensured that the MS reports only theinformation of the cells that may become the targethandover cells, instead of indiscriminately according tothe signal level only. Usually, the MS should be made not

17


to report the cells of other GSMPLMNs. The above functioncan be implemented by restricting the MS to measure onlythe cells whose NCCs are some fixed values. The NCCPERMprovides the NCCs of the cells that the MS needs tomeasure.

The BSIC is transmitted continuously on the SCH of eachcell, while the higher three bits of the BSIC representthe NCC, so the MS only needs to measure the NCC of theadjacent cell and compare the result with the PLMNparameter. If the NCC is within the set, it reports theresult to the BTS. Otherwise, it discards the measurementresults.

2.6.2 Format

This parameter is a decimal number, in the range of 0 ~ 7.When the NCCPERM is set to a value, it means that the BTSneeds to measure the cell whose NCC is that value.


In China, usually each area is assigned with one ormultiple NCCs, and the NCCPERM parameter of all the cellsin the area must include the NCC of the local area.Otherwise, enormous inter-cell call drop and cellreselection failure may occur. In addition, to ensure thatnormal roaming between areas, the edge cells of an areashould include the NCC of the adjacent areas.

2.6.4 Precautions

The inappropriate setting of this parameter may be one ofthe major reasons call drop.

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2.7 Cell Bar Access (CBA)

2.7.1 Definition

In the system message broadcast in each cell, there is abit used to indicate if the cell allows the access of MS,or, cell bar access. The CB parameter is used to indicatewhether the cell is set with the cell bar access.

2.7.2 Format

The parameter is represented in a character string, withthe following values:

YES: Enable CBA.

NO: Disable CBA.

The default value is NO.


The CBA bit is a parameter that the network operator canset. Usually, all cells allow MS access, so the bit shouldbe set to NO. However, in special cases, the carrier maywant to use a cell for handover only. Such a need can beimplemented by setting the parameter to YES.

2.7.4 Precautions

The CBA is only applicable to some special cases, and itshould be set to NO for common cells.

2.8 Cell Bar Qualify (CBQ)

2.8.1 Definition

For an area covered by cells in an overlay way, accordingto the capacity of each cell, traffic volume and thefunctionality difference of various cells, the carrier

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usually wants the MS to first select some cells in cellselection, by setting priorities for the cells. Thisfunction can be implemented by setting the CBQ parameter.

2.8.2 Format

The CBQ is represented as a character string, with thevalues of HIGH and LOW, defaulted to HIGH. The CBQ and theCBA together determine the priority status of a cell, asshown in Table 2.8 -4.

Table 2.8-4 Parameter CBQ

Cell BarQualify

Cell BarAccess

Cell SelectionPriority

Cell ReselectionStatus

NO NO Normal NormalNO YES Prohibited ProhibitedYES NO Low NormalYES YES Low Normal

In the above table, there is one exception that the cellselection priority and cell reselection status should benormal when the following conditions are met at the sametime:

1. The cell belongs to the home PLMN of the MS.

2. The MS is in the cell test operation mode.

3. The CBA of the cell is YES.

4. The CBQ is NO.

5. The access control level 15 is disabled.


Usually, the priority should be set to “Normal”, that is,CBQ=0, for every cell. But in some cases, such as microcellular application, dual-frequency networking, carriersmay hope that the MS preferably enters some types of cells

20


first. Then, the network operator can set the priority ofthis cell type to “Normal”, while setting the prioritiesof other cells to “Low”.

During the cell selection process of the MS, only when noappropriate cell with priority of Normal exists (byappropriate, it means that various parameters meet theconditions of cell selection, that is, C1>0 and the celldoes not prohibit access), will the cells with lowerpriorities be selected.

2.8.4 Precautions

Note that when you optimize the network by using the cellpriorities, the CBQ affects only cell selection, whilehaving no impact on cell reselection. Therefore, toachieve the objective, you must use the CBQ and C2 incombination.

2.9 Access Control Level (AC)

2.9.1 Definition

In some special cases, the carrier wants to prohibit allor some MSs from initiating access requests or pagingresponse requests in some special areas. for example, whenemergencies occur in some areas or one GSM PLMN hascritical faults. Therefore, the GSM specification (02.11)stipulates that one access level should be allocated toeach GSM subscriber (common subscriber) usually. Theaccess level is available in 10 brackets from 0 to 9,which are stored in the SIM cards of the mobilesubscribers. For some special subscribers, the GSMspecification reserves five special access levels, 11 to15. These levels usually have higher access priorities.These special subscribers can have one or multiple accesslevels at the same time (11 ~ 15), which are also stored

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in the SIM cards of the subscribers. The access levels areallocated as below:

Levels 0 ~ 9: common subscribers

Level 11: for management of the PLMN

Level 12: for use by security departments

Level 13: for pubic utilities (water, gas and so on)

Level 14: emergency services

Level 15: PLMN employees

Subscribers with access levels 0 ~9 have access to boththe home PLMNs and visited PLMNs. Subscribers with accesslevels 11 and 15 have access to only the home PLMNs.Subscribers with access levels of 12, 13 and 14 haveaccess within the country of the home PLMN.

Subscribers with access levels 11 ~ 15 have higher accesspriorities than subscribers with access levels 0 ~ 9, butwithin access levels 0~9 and access levels 11 ~ 15, themagnitudes of the numbers do not represent difference inpriorities.

2.9.2 Format

The access level control parameter consists of 16 bits. Ifone bit is 0, it means that the MSs with the appropriateaccess level are not allowed to access the current cell.Otherwise, access is allowed.


C0 ~ C15 (excluding C10) can be set by the networkoperator, and should usually be set to 1. Appropriatelysetting these bits have very important influence fornetwork optimization, in the following aspects:

1. During the installation and commissioning of the BTS

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or during the maintenance and test of some cells, theoperator can set C0 ~ C9 to 0, to forcedly prohibitthe access of common subscribers, thus reducing theunnecessary impact on the installation andmaintenance.

2. For cells with heavy traffic, congestion may occurduring busy hours, with the symptoms of increasedRACH conflicts, AGCH flow overload, and Abisinterface flow overload. In the GSM specification,there are many means to solve overload andcongestion, but most of them will affect theutilization of the equipment resource. The networkoperator can control the traffic volume in a cell bysetting the appropriate access control parameter (C0~ C15). For example, when a cell experiences trafficoverload or congestion, you can set Ci to 0 toprohibit the MSs of the appropriate access level fromaccessing the current cell (The change of the Ci doesnot affect the MSs in communication), to reduce thetraffic volume in the cell. The disadvantage of theabove mode is that some MSs are treated “unfairly”.To solve this problem, you can change the values ofC0 ~ C9 of the cell in cycle, at an interval of fiveminutes, for example, to access the MSs with even orodd levels alternately.

2.9.4 Precautions

The value of the Ci does not affect the cell selection andreselection process of the MS.

2.10 MAX RETRANS

2.10.1 Definition

When a MS starts the immediate assignment process (such as23


the MS needs to update the location, originate a call orrespond to paging), it will send the “channel request”message over the RACH channel to the network. Because theRACH is an ALOH channel, the network allows the MS to sendmultiple channel request messages before receiving theimmediate assignment message, to improve the success ratioof MS access. The MAX RETRANS is determined by thenetwork.

2.10.2 Format

The MAX RETRANS is represented as a decimal number, whichcan be 1, 2, 4 or 7, as shown in Table 2.10 -5.

Table 2.10-5 Codes of the MAX RETRANS (M)

M Code MAX RETRANS00 101 210 411 7


The MAX RETRANS of each cell in the network can be set bythe network operator. Usually, the larger the MAX RETRANS,the higher the call attempt success ratio and callcompletion ratio, but also the higher the load on theRACH, CCH and SDCCH. In the cells with heavy traffic, ifthe MAX RETRANS is too high, overload and congestion ofradio channels may occur, thus greatly reducing the callcompletion ratio and radio resource utilization. On thecontrary, if the MAX RETRANS is too low, the call attemptsuccess ratio of the MS will decrease, thus affecting thecall completion ratio of the network. Therefore,reasonably setting the MAX RETRANS of each cell is animportant means to fully exploit the network radio

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resources and improve the call completion ratio. You canobserve the following principles in setting the MAXRETRANS (M):

1. For the areas with cell radius over 3 Km and lowtraffic (usually suburbs or rural areas), the MAXRETRANS can be set to 11 (that is, the maximum numberof retransmissions is 7) to improve the accesssuccess ratio of the MS.

2. For the areas with cell radius below 3 Km and commontraffic (non-busy areas in cities), the MAX RETRANScan be set to 10 (that is, the maximum number ofretransmissions is 4).

3. For micro cells, it is recommended to set the MAXRETRANS to 01 (that is, the maximum number ofretransmissions is 2).

4. For the micro cells with heavy traffic and the cellswith obvious congestion, it is recommended to set theMAX RETRANS to 00 (that is, the maximum number ofretransmissions is 1).

2.11 Transmission Distribution Timeslots (Tx_integer)

2.11.1 Definition

If the RACH in the GSM system is an ALOH, the GSMspecification (section 3.3.1.2, 04.08) stipulates that theMS must use the access algorithm to reduce the number ofconflicts on the RACH for MS access and improve theefficiency of the RACH channel. This algorithm uses threeparameters: Tx_integer, MAX RETRANS and the parameter Srelated to Tx_integer and channel combination.

The MAX RETRANS has already been described in othersections in this document. The Tx_integer parameter is the

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interval in timeslots at which the MS continuously sendsmultiple channel request messages. The parameter S is anintermediate variable in the access algorithm, and is tobe determined by the Tx_integer parameter and thecombination mode of the CCCH and SDCCH.

2.11.2 Format

The Tx_integer is a decimal number, which can be 3~12, 14,16, 20, 25, 32 and 50 (default). The values of theparameter S are shown in Table 2.11 -6.

Table 2.11-6 Values of the Parameter S

Tx_integerCCH Combination Mode

CCCH Not Shared withSDCCH

CCCH Shared with SDCCH

3, 8, 14, 50 55 414, 9, 16, 76 525, 10, 20, 109 586, 11, 25, 163 867, 12, 32, 217 115


When a MS accesses the network, it needs to initiate animmediate assignment process. At the start of thisprocess, the MS will send (MAX RETRANS+1) channel requestmessages over the RACH. To reduce the number of conflictson the RACH, the MS must send the channel request messagesat the time according to the following rules:

1. The number of timeslots between the time when the MSstarts the immediate assignment process and the timewhen the first channel request message is sent(excluding the timeslot at which the message is sent)is a random number. This random number is an elementin the {0, 1, ..., MAX (Tx_integer, 8)-1} set. Every

26


time when the MS starts the immediate assignmentprocess, it takes a number from the above setaccording to the even distribution probability.

2. The number of timeslots between any two adjacentchannel request messages (excluding the timeslot atwhich the message is sent) is taken by the MS fromthe {S, S+1, ..., S+Tx_integer-1} set according tothe even distribution probability.

According to the above analysis, the larger the Tx_integerparameter, the larger the change in the interval at whichthe MS sends channel request messages, while the smallerthe number of RACH conflicts. The larger the S parameter,the larger the interval at which the MS sends channelrequest messages, and the fewer the conflicts on the RACH,and the higher the utilization of the AGCH and SDCCH.Every time the network receives one channel request, itallocates one signaling channel as long as there are anyidle channels available, regardless whether the channelrequest message is sent by the same MS. However, as theTx_integer and S become greater, the access time of the MSis prolonged, thus degrading the access performance of theentire network, so appropriate Tx_integer and S must beselected.

The parameter S is actually calculated by the MS accordingto the Tx_integer parameter and the combination of theCCCH, while the Tx_integer parameter is periodically sentin the system messages broadcast by the cell. The networkoperator can set the appropriate Tx_integer value for thebest access performance of the network according to theactual application of the system. You usually can observethe following principles in selecting the value for theTx_integer:

1. Usually, you should select a value for the Tx_integer

27


that makes the smallest possible parameter S (toreduce the access time of the MS), but you mustensure that the AGCH and SDCCH are not overloaded.During operation, you can select any Tx_integer valuefor the cells with traffic volume unknown to make thesmallest parameter S. If the AGCH or SDCCH of thecell is overloaded, you should change the TX toincrease the parameter S until the AGCH or SDCCH isno longer overloaded.

2. According to the above principles, you can determinethe value range of the Tx_integer (for each value ofthe parameter S, the TX parameter can have multiplevalues). When there are many RACH conflicts in thecell, the larger Tx_integer value (within the aboverange) should be taken. When there are few RACHconflicts (quantitative analysis should be performedafter experiment), the value of the Tx_integer shouldbe as small as possible.

2.12 IMSI Attach/Detach Permission (ATT)

2.12.1 Definition

The IMSI detach process is the process that the MSnotifies the network that it is leaving from the workingstatus to the non-working status (usually the power-offprocess), or that the SIM card has been removed from theMS. When the network receives such a notification from theMS, it will indicate that the IMSI subscriber is in thenon-working status, so the connection request with thesubscriber as the called party will be rejected. Theopposite process is the attach process that the MSnotifies the network that it is entering the workingstatus (usually the power-on process), or that the SIMcard is inserted into the MS again. When the MS enters the

28


working status again, it will detect whether the currentLocation Area Identity (LAI) matches the LAI last recordedin the MS. If they match, the MS will start the IMSIattach process. Otherwise, the MS starts the locationupdate process (instead of the IMSI attach process). Afterthe network receives the location update or IMSI attachprocess, it will indicate that the IMSI subscriber is inthe working status.

The ATT parameter is used to notify the MS that whetherIMSI attach and detach processes are allowed in thecurrent cell.

2.12.2 Format

The ATT is represented as a character string, with thefollowing values:

NO: It means that the MS is not allowed to start the IMSIattach and detach processes.

YES: It means that the MS must start the IMSI attach anddetach processes.


The ATT flag is usually set to be YES, so that the networkdoes not handle the connection processes with thesubscriber as the called party when the MS is turned off.This saves not only the processing time of variousentities of the network, but also many resources of thenetwork (for example, paging channel).

2.12.4 Precautions

When you set the ATT, you must note that the setting ofthe ATT must be the same for different cells of the samelocation area. This is because that the MS starts the IMSIdetach process when it is powered off in the cell whose

29


ATT is set to YES, and the network will record the non-working status for the subscriber and reject all theconnection requests with the subscriber as the calledparty. If when the MS is powered on again in the samelocation area where it has been powered off (so nolocation update process is initiated), but in anothercell, while the ATT of the cell is set to NO, the MS alsodoes not initiate the IMSI attach process. In this case,the subscriber cannot be called normally until itinitiates the location update process.

2.13 Periodical Location Update Timer (T3212)

2.13.1 Definition

In the GSM system, location update will occur in thefollowing two cases: (1) The MS detects that it is inanother location area (different LAC), and (2) The networkrequires the MS to perform location update at regularintervals. The frequency of periodical location update iscontrolled by the network, or precisely, according to theT3212 parameter.

2.13.2 Format

The T3212 is a decimal number, within the range of 0~255,in the unit of six minutes (1/10 hours). For example, ifT3212=1, it means 0.1 hours. If T3212=255, it means 25hours and 30 minutes.

If the T3212 is set to 0, it means that the cell needs noperiodical location update.


The periodical location update is an important means forthe close relation between the network and mobile

30


subscribers. Therefore, the shorter the periodicallocation update interval, the better the overallperformance of the network. However, frequent periodicalupdate has two adverse side effects. One is much moresignaling flows in the network and reduced utilization ofradio resources, and affected processing capability ofvarious entities of the system in worst cases (includingMSC, BSC and BTS). On the other hand, it increases thepower consumption of the MS, greatly reducing the averagestandby time of the MSs in the system. Therefore, theT3212 should be set by considering the utilization of thevarious resources of the network.

The 3212 can be set by the network operator, and itsspecific value depends on the flows and processingcapabilities of various parts in the system. Usually, youare recommended to use a large T3212 (for example, 16hours, 20 hours, or even 25 hours) in the areas with heavytraffic and signaling flows, and use a small T3212 (forexample, 3 hours, and 6 hours) in the areas with lowsignaling traffic. For the areas where the traffic volumeis far above the system capacity, you are recommended toset the T3212 to 0. To set the T3212 to an appropriatevalue, you should perform a comprehensive and long-termmeasurement of the processing capabilities and flows ofvarious entities of the system on the running network (forexample, processing capabilities of the MSC and BSC, Ainterface, Abis interface, Um interface, and HLR, VLR).When any of them is overloaded, you may increase the valueof the T3212.

2.13.4 Precautions

The T3212 should not be set to too low a value, as thisnot only increases the signaling flows on variousinterfaces of the network and also sharply increases the

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power consumption of the MS (particularly handset). TheT3212 lower than 30 (except 0) may produce a disastrousimpact on the network.

2.14 Multi-band Indication (MBCR)

2.14.1 Definition

In a single-band GSM system, when a MS reports themeasurement result of the adjacent cells to the network,it only needs to report the contents of the six adjacentcells with the most powerful signals in a frequency band.For multi-band networking, the carries hope that the MSwill enter a certain frequency band preferably duringinter-cell handover according to the actual networksituations. Therefore, it is hoped that the MR reportingof the MS is not only based upon signal strength, but alsobased upon the signal frequency band. The parameter Multi-band Indication (MBCR) is used to indicate to the MS thatit needs to report contents of the adjacent cells ofmultiple bands.

2.14.2 Format

The MBCR is a decimal number, within the range of 0 ~ 3.Its meaning is described as below:

0: According to the signal strength of the adjacent cells,the MS need to report the measurement results of the sixadjacent cells with the highest signal level and withknown and allowed NCC, regardless of the band the adjacentcells are located.

1: The MS needs to report the measurement result of oneadjacent cell at each band (not including the band used bythe current service cell) with highest signal level andknown and allowed NCC included in the adjacent cell table.

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The adjacent cell at the band of the current service areawill be reported in the remaining position. If there aresill remaining positions, the conditions of other adjacentcells will be reported (regardless of frequency band).

2: The MS needs to report the measurement results of twoadjacent cells at each band (not including the band usedby the current service cell) with highest signal level andknown and allowed NCC included in the adjacent cell table.The adjacent cell at the band of the current service areawill be reported in the remaining position. If there aresill remaining positions, the conditions of other adjacentcells will be reported (regardless of frequency band).

3: The MS needs to report the measurement results of threeadjacent cells at each band (not including the band usedby the current service cell) with highest signal level andknown and allowed NCC included in the adjacent cell table.The adjacent cell at the band of the current service areawill be reported in the remaining position. If there aresill remaining positions, the conditions of other adjacentcells will be reported (regardless of frequency band).



The value range of MBCR is 0 to 3. In the multi-bandapplication environment, its value is related to theservice traffic at each band. Generally, please refer tothe following principles in setting the value:

1. If the traffic of each band is basically the same,then when the carrier does not need band selectivity,please set the MBCR to “0”.

2. If the traffic of each band is obviously differentand the carrier hopes that the MS enters a certainband preferably, then please set the MBCR to “3”.

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For the case between the above two conditions, please setthe MBCR to “1” or “2”.

2.15 CLASSMARK Early Sending Control (ECSC)

2.15.1 Definition

For each MS, there is some information about the MScapability, for example, the power level of the MS, thesupported encryption algorithm, and whether the MSoriginated short messages are supported. Such informationis referred to as the CLASSMARK of the MS, and is usuallystored in the database of the network. In a single-bandnetwork, the CLASSMARK of an MS is often constant. Whenthe MS accesses the network for services, the networkqueries such information in the database without needingthe MS to report them. If such data of the MS has changedor the network queries the MS for the CLASSMARK, the MSwill notify the network of its CLASSMARK through theCLASSMARK CHANGE message.

As the dual-band networks appear, dual-band handsetsemerge accordingly. In different bands, one handsetusually has different CLASSMARKs, for example, the powerlevel. When the MS accesses the network, the network isnot clear about the current band at which the MS isworking, so it has no way to obtain the MS of theCLASSMARK. This will inevitably cause the case that thenetwork has to query the handset for its CLASSMARK everytime it accesses the network. Therefore, GSM Phase2plusprovides the additional “CLASSMARK early sending” option.When the network uses this option, the handsets supportingthis option will send the CLASSMARK CHANGE message to thenetwork as earlier as possible after it accesses thenetwork. This avoids the query process of the network.

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2.15.2 Format

The parameter is represented as a character string, to beYES or NO, which means:

YES: The cell uses the “CLASSMARK early sending” option.

NO: The cell does not use the “CLASSMARK early sending”option.


This function is developed to accommodate dual-bandnetworking, so you are recommended to set this parameterto NO for single-band networking. In the case of dual-bandnetworking and that dual-band handsets are allowed toswitch over between the dual-band networks, you should setthis parameter to YES, to reduce the signaling flows.

2.15.4 Precautions

In the case of dual-band networking, the parameter shouldbe set to the same value for all the cells in the network.One or multiple cells should not have a different valuefor this parameter, to avoid the degrade of the networkquality.

2.16 Wait Indication T3122

2.16.1 Definition

After the network receives the channel request messagefrom the MS, if there is no proper channel to be allocatedto the MS, the network will send the “immediate assignmentreject message” to the MS. To avoid the MS continuouslysending the channel request that will result in furthercongestion of the radio channel, the timer parameter T3122will be contained in the “Immediate assignment rejectmessage”, that is, the waiting indication information

35


unit. After receiving the “immediate assignment rejectmessage”, the MS must wait for a period indicated by theT3122 before starting a new call.

2.16.2 Format

The timing length of the T3122 is 0 ~ 255 seconds.


In fact, the T3122 determines the time the MS must waitbefore it can initiate another call attempt following acall attempt failure, when the radio resource isinsufficient in the network. Therefore, its value has ahuge impact on the network performance. If the T3122 isset to too low a value, the channel may be furthercongested when the radio channel load is large. On theother hand, if the T3122 is set to too high a value, theaverage access time of the network will increase, causingdegrade in the average service performance of the network.

The principles for setting the T3122 are: On theprecondition that the CCCH is not overloaded in thenetwork, the T3122 should be as small as possible, usuallyto 10 ~15 seconds. In the area with heavy traffic, itshould be set to 15 ~ 25 seconds.

2.16.4 Precautions

In a cell, the T3122 can be adjusted dynamically.

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3 Cell Selection Parameter

After a MS is turned on, it will attempt to contact acommon GSM PLMN, so the MS will select an appropriatecell, and extract from it the parameters of the controlchannel and the prerequisite system information. Such aselection process is referred to as cell selection. Thequality of a radio channel is an important factor of cellselection. The GSM specification defines the path losscriterion C1, and such appropriate cell must ensure thatC1>0. The C1 is calculated according to the followingformula:

C1=RXLEV-RXLEV_ACCESS_MIN-MAX((MS_TXPWR_MAX_CCH-P), 0)

Where:

The RXLEV is the average reception level.

The RXLEV_ACCESS_MIN is the minimum level at which the MSis allowed to access.

The MS_TXPWR_MAX_CCH is the maximum power level of theCCH.

The “P” is the maximum transmitted power of the MS.

MAX (X, Y) = X; If X Y.

MAX (X, Y) = Y; If Y X.

After the MS selects a cell, it will stay in the selectedcell if no major changes have occurred to variousconditions.

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3.1 RXLEV_ACCESS_MIN

3.1.1 Definition

If the MS is accessed to the system when the receptionsignal level is very low (the communication quality afteraccess usually cannot ensure a normal communicationprocess), the network cannot provide satisfactorycommunication quality to the user and the radio resourcesare wasted. To prevent such access, the GSM systemstipulates that if a MS wants to access the network, itsreception level must be greater than a threshold level,that is, the RXLEV_ACCESS_MIN.

3.1.2 Format

The RXLEV_ACCESS_MIN is a decimal number, within the rangeof 47 ~ 110. It is defaulted to 110, and its meaning isshown in Table 3.1 -7.

Table 3.1-7 Code of the RXLEV_ACCESS_MIN Parameter

RXLEV_ACCESS_MIN Meaning47 > -48 dBm (level 63)48 -49 ~ -48 dBm (level 62)... ...108 -109 ~ -108 dBm (level 2)109 -110 ~ -109 dBm (level 1)110 <-110 dBm (level 0)


The RXLEV_ACCESS_MIN can be set by the network operator.Its settings comply with the requirements of the path losscriterion C1. Usually, its value should be close to thereception sensitivity of the MS. Since theRXLEV_ACCESS_MIN also affects the cell selection parameterC1, it is of vital importance to flexibly set the

38


parameter for the balanced network traffic and networkoptimization.

For a cell with traffic overload, you can appropriatelyincrease the RXLEV_ACCESS_MIN of that cell, so that the C1and C2 of the cell become smaller, and the coverage areaof the cell will decrease accordingly. However, theRXLEV_ACCESS_MIN value cannot be set to too high a value.Otherwise, “blind areas” will be caused on the borders ofcells. With this measure for traffic balance, it issuggested that the RXLEV_ACCESS_MIN value should notexceed -90 dBm.

3.1.4 Precautions

Except the areas with dense BTSs and good radio coverage,you are usually recommended to use the RXLEV_ACCESS_MIN toadjust the traffic volume of the cell.

3.2 Cell Selection Hysteresis

3.2.1 Definition

When a MS reselects a cell, if the source cell and targetcell belong to different areas, the MS should initialize alocation update process after reselecting the cell. Due tothe fading characteristic of the radio channel, normally,the C2 values of two cells measured at the adjacent cellboundary will have relatively great fluctuation, causingthe MS to frequently reselect cells. Although the intervalof reselecting two cells by the MS will not be less than15s, it is extremely short for location update. It notonly dramatically increases the signaling flow ofnetworks, while the radio resources can not be fullyutilized, but also decreases the call completion ratio ofthe system due to the failure to respond to the pagingduring the location update process. To reduce the impact

39


of this problem, the GSM specification has set aparameter, known as cell selection hysteresis. Theadjacent cell (whose location is different from thecurrent area) must have a signal level greater than thecurrent cell, and the difference must be greater than thespecified cell selection hysteresis, before the MS caninitiate cell reselection.

3.2.2 Format

The cell selection hysteresis is a decimal number, in dB,within the range of 0 ~ 14, at the step of 2 dB, defaultedto 4.


After the appropriate cell selection hysteresis isselected, the level has importance significance fornetwork optimization.

You are usually recommended to set the cell selectionhysteresis to 8 dB or 10 dB. In the following cases, youare recommended to make appropriate adjustment:

1. When there is very large traffic in an area and theoverload of signal flow frequently occurs, it issuggested to increase the cell selection hysteresisof adjacent cells with different LACs in the area.

2. When the overlapped coverage of the adjacent cellsbelonging to different location areas is rather big,it is suggested to increase the cell selectionhysteresis parameter.

If the coverage at the borders between the adjacent cellsof different LACs is poor, that is, “seam” of coverage, orthe border is located in the place with few objects inslow motion like highways, you are recommended to set thecell selection hysteresis to 2 ~ 6 dB.

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3.2.4 Precautions

Except in special cases, it is recommended that thisparameter should not be set to 0 dB.

3.3 Cell Reselection Offset (CRO), Temporary Offset(TO) and Penalty Time (PT)

3.3.1 Definition

After a MS selects a cell, the MS will stay in theselected cell as long as no major changes occur to variousconditions. At the same time, the MS starts to measure thesignal level of the BCCH carrier of the adjacent cells,records the six adjacent cells with the highest signallevels, and extracts from them the various system messagesand control messages of each adjacent cell. When theappropriate conditions are met, the MS will switch fromthe current cell to another cell, a process known as cellreselection. Such appropriate conditions include multiplefactors, including cell priority, and whether the cell isprohibited from access. Among them, an important factor isthe quality of the radio channel. When the signal qualityof the adjacent cell exceeds that of the current cell,cell reselection is triggered. For cell reselection, thechannel quality criterion is determined by the C2parameter, which is calculated according to the followingformula:

C2 = C1 + CELL_RESELECT_OFFSET - TEMPORARY_OFFSET × H(PENALTY_TIME-T)

When the PENALTY_TIME is not equal to 31;

C2 = C1 - CELL_RESELECT_OFFSET

When the PENALTY_TIME is equal to 31;

Where:

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1. H (x) = 0, when x<0; H (x) = 1, when x0

2. T is a timer with the initial value of 0. When a cellis recorded on the list of the six adjacent cellswith the highest signal level by the MS, the timer Tof that cell starts to count to the accuracy of aTDMA frame (about 4.62 ms). When the cell is deletedfrom the list of the six adjacent cells with thehighest signal level by the MS, the correspondingtimer T will be reset.

3. The CELL_RESELECT_OFFSET is used to correct the cellreselection parameter C2.

4. The function of the TEMPORARY_OFFSET is to give theC2 a negative correction during the period betweenwhen the timer T starts and when it reaches thespecified value of the PENALTY_TIME.

5. The PENALTY_TIME is the time that theTEMPORARY_OFFSET works on the C2 parameter. However,the all 1’s code of the PENALTY_TIME is reserved forthe CELL_RESELECT_OFFSET to change the sign for theeffect on the C2.

6. The CELL_RESELECT_OFFSET, TEMPORARY_OFFSET andPENALTY_TIME are cell reselection parameters. Whenthe cell reselection parameter indication (PI) is 1,they are broadcast on the BCCH of the cell. If PI=0,the MS believes that they are all 0, and hence C2=C1.

If the MS finds that the C2 value of an adjacent cell (thecurrent cell is in the same location area) exceeds the C2value of the current cell and this continues for more thanfive minutes, then the MS will start the cell reselectionprocess to enter the adjacent cell. If the MS finds that acell in another location area different from the currentcell has a C2 value exceeding that of the current valueplus the cell selection hysteresis and this continues for

42


more than five minutes, then the MS will start the cellreselection process to enter the adjacent cell. However,it must be noted that the cell reselection initiated bythe C2 parameter should be at an interval of at least 15seconds, to avoid frequent cell reselection of the MS.

The cell reselection initiated by the cell channel qualityuses the C2 parameter as the criterion. The C2 is based onthe C1 parameter, with some manual offset parametersincorporated. The manual effect is incorporated toencourage the MS to first enter some cells or prevent itfrom entering them. Usually, such means are used tobalance the traffic volume in the network.

In addition to the C1 that affects the C2 parameter, thereare the following three factors: CELL_RESELECT_OFFSET(CRO), TEMPORARY_OFFSET (TO) and PENALTY_TIME (PT).

The CRO is a value of quantity, meaning the manualcorrection value to the C2. The TO means the temporarycorrection value for the C2. By temporary, it means thatthe value only takes effect on the C2 within a certainperiod, which is determined by the PT parameter.

3.3.2 Format

The CRO is a decimal number, in dB, within the range of 0~ 63, meaning 0 ~ 126 dB, at the step of 2 dB. Its defaultvalue is 0.

The TO is a decimal number, in dB, within the range of 0 ~7, meaning 0 ~ 70 dB, at the step of 10 dB, where 70 meansinfinite. Its default value is 0.

The PT is a decimal number, in seconds, within the rangeof 0 ~ 31, meaning 20 ~ 620 seconds for 0 ~ 30, and at thestep of 20 seconds. The value of 31 is reserved to changethe direction of effect that the CRO works on the C2parameter. Its default value is 0.

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3.3.3 Precautions

You should pay attention to the following problems whenyou adjust the above parameters:

1. In whatever conditions, you are not recommended toset the CRO to a value higher than 25dB, because thetoo high CRO may cause instability to the network.

2. The above parameters are set on the basis of eachcell. However, due to the nature of the C2 parameterand its close relationship with the adjacent cell,you should pay attention to the relationship betweenthe adjacent cells when you set these parameters.

3.4 MS_TXPWR_MAX_CCH

3.4.1 Definition

During the communication between the MS and the BTS, thetransmitted power of the MS is controlled by the network.The network sets the power of the MS by using the PowerCommand, which is transmitted over the SACCH. The MS mustextract the power control header from the downlink SACCHand takes the specified transmitted power as the outputpower. If the power level of the MS cannot output thepower value, it will output the closest transmitted powerthat can be outputted.

Because the SACCH is the channel associated signaling, itmust be used in combination with other channels such asSDCCH and TCH. Therefore, the power control of the networkover the MS actually starts when the MS receives theSACCH. The power of the MS before it receives the SACCH(the power used to send the RACH) is determined by themaximum power level of the control channel(MS_TXPWR_MAX_CCH).

The principle for setting the control channel power level44


is: on the precondition that the MS on the edge of thecell has appropriate access success ratio, the accesslevel of the MS should be as low as possible. Obviously,the larger the coverage area of a cell, the higher thepower level that the MS must output. Usually, you arerecommended to set this parameter to 33 dBm for GSM900 MSand 26 dBm for GSM1800 MS). In actual applications, afterthe parameter is set, you can make a dial test at the cellboundary to test the MS access success rate and accesstime with different parameter settings to determinewhether to increase or decrease the value of thisparameter.

3.4.2 Format

The MS_TXPWR_MAX_CCH is a decimal number, in dBm, withinthe following range:

GSM900 system: 5 ~ 39 dBm, odd numbers

GSM1800 system: 0 ~ 30 dBm, even numbers


The MS_TXPWR_MAX_CCH is set to control the interferencebetween adjacent cells. If this parameter is too large,the interference between adjacent cells increases. If thisparameter is too small, the MS on the cell edge may have alow access success ratio.

The principle for setting this parameter is: under theprecondition that the MS on the cell edge has anappropriate access success ratio, the access level of theMS should be reduced as far as possible. Obviously, thelarger the coverage area of a cell, the higher the powerlevel that the MS must output.

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3.5 Cell Reselection Parameter Indication (PI)

3.5.1 DefinitionThe cell reselection parameter indication (PI) is used tonotify the MS whether to use the C2 as the cellreselection parameter and if there is the parameter forcalculating C2.

3.5.2 FormatThe PI consists of only one bit, where “1” indicates thatthe MS should extract parameters from the system messagesbroadcast by the cell to calculate the value C2 as thecell reselection criterion. “0” indicates that the MSshould use C1 as the criterion for cell reselection (it isequivalent that C2=C1).

3.5.3 Setting and InfluenceIf C2 is used as the cell reselection parameter, the PImust be set to 1. Otherwise, it must be set to 0.

3.6 Additional Reselection Parameter Indication (ACS)

3.6.1 DefinitionThe ACS is used to notify a MS whether to use C2.

3.6.2 FormatThe ACS consists of only one bit, whose meaning isdescribed as below:

1. In system message 3, the ACS is meaningless, and theequipment manufacturer should set the bit to 0.

2. In system message 4, when ACS=0, it means that ifsystem message 4 has any remaining byte, the MSextracts from it the PI parameter about cellreselection and the related parameters for

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calculating C2. When ACS=1, it means that the MSextracts from the remaining byte of system messages 7or 8 the PI parameter about cell reselection and therelated parameters for calculating C2.

3.6.3 Setting and InfluenceIn the configuration of common cells, system messages 7and 8 are seldom used, so the ACS should usually be set to0.

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4 Network Function Parameters

4.1 MS Dynamic Power Control Status

4.1.1 DefinitionTo minimize the interference of the radio space at acertain communication quality, the GSM system provides thepower control capability for the MS. Whether power controlis used can be determined by setting the “MS dynamic powercontrol status” parameter.

4.1.2 Format

This parameter is an identifier, which can be ACTIVE orINACTIVE, with the following meaning:

ACTIVE: The MS uses dynamic power control.

INACTIVE: The MS does not use dynamic power control.

4.1.3 Setting and InfluenceMS dynamic power control can reduce the radio interferencein the network and increase the service quality of thenetwork, so usually the MS power control should be used,by setting the parameter to ACTIVE.

4.2 Frequency Hopping Status (H)

4.2.1 DefinitionAccording to the GSM specification, the GSM radioequipment should support the frequency hopping function.Theoretical analysis shows that frequency hopping canimprove the frequency spectrum environment in the space

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and elevate the communication quality of the entirenetwork. Whether frequency hopping is used in the networkcan be implemented by setting the “frequency hoppingstatus (H)” parameter.

4.2.2 FormatThis parameter is represented by one bit, where 0 meansthat frequency hopping is disabled, and 1 means thatfrequency hopping is enabled.

4.2.3 Setting and InfluenceWhen conditions are mature, the operation department isrecommended to use the frequency hopping function.

4.3 Hopping Sequence Number (HSN)

4.3.1 DefinitionIn the GSM system, the set of carriers used by each cellis expressed as “Cell Allocation (CA)”, written as {R0,R1, …, RN-1}, where Ri means the absolute frequency number.For each communication process, the set of carriers usedby the BTs and MS is expressed as “Mobile Allocation(CA)”, written as {M0, M1, …, MN-1}, where Mi means theabsolute frequency number. Obviously, the MA is a subsetof the CA.

During the communication process, the carrier number usedon the air interface is an element in the MA set. Thevariable “Mobile Allocation Index (MAI)” is used todetermine an exact element in the MA set, where0 M A I n - 1 . According to the frequency hoppingalgorithm given in GSM 05.02, the MAI is the function ofthe TDMA FN (RFN), HSN, and MAIO. Where, the HSNdetermines the track for the running of the frequencypoint during frequency hopping. That the adjacent uses thecells with the same MA and takes different HSNs can ensure

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that the utilization of frequencies is not in conflictduring the frequency hopping process.

4.3.2 FormatThis parameter is a decimal number, in the range of 0 ~63, where:

0: cyclic frequency hopping

1~63: pseudo random frequency hopping

4.3.3 Setting and InfluenceThe cells using frequency hopping can have any HSNs, butthe cells in the same frequency group must use differentHSNs.

4.4 Mobile Allocation Index Offset (MAIO)

4.4.1 DefinitionDuring the communication process, the carrier number usedon the air interface is an element in the MA set. Thevariable “Mobile Allocation Index (MAI)” is used todetermine an exact element in the MA set, where0 M A I n - 1 . According to the frequency hoppingalgorithm given in GSM 05.02, the MAI is the function ofthe TDMA FN (RFN), HSN, and MAIO. Where, the MAIO is aninitial offset of the MAI, used to prevent multiplechannels from seizing the same carrier at the same time.

4.4.2 FormatThis parameter is a decimal number, in the range of 0 ~63.

4.4.3 Setting and InfluenceIt should be noted that the channels on the same carrierin a cell should have the same MAIO. In addition, the

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different cells with the same group of MA should also havethe same MAIO.

4.5 Discontinuous Transmission (DTX)

4.5.1 DefinitionDiscontinuous transmission (DTX) refers to the process thatthe system does not transmit signals in the speech pauseperiod during the subscriber communication process.

4.5.2 FormatThe network operator can set whether DTX is allowed in thenetwork by setting the DTX parameter. This parameter is adecimal number, within the range of 0 ~ 2, with themeaning described as below:

0: The MS can use uplink DTX.

1: The MS should use uplink DTX.

2: The MS cannot not use uplink DTX.

4.5.3 Setting and InfluenceThe use of the DTX only has a very limited impact on thecall quality, while it has two advantages: (1) Theinterference of radio channels is effectively reduced, sothe average call quality of the network is improved. (2)It greatly saves the power loss of the MS. Therefore, theDTX is recommended on the network.

4.6 Average Cycle of Idle Channel Interference Level(INTAVE)

4.6.1 DefinitionAccording to GSM 05.08, the BTS must measure the uplinkinterference level of all idle channels, to provide the

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basis for management and allocation of radio resources.Due to the randomness of the radio channel interference,the BTS must average the measured uplink interferencelevels within the specified period, and this average cycleis determined by the INTAVE parameter.

4.6.2 FormatThis parameter is a decimal number, in SACCH multi-frames,within the range of 1 ~ 31.

4.6.3 Setting and InfluenceThe smaller the INTAVE, the more real-time themeasurement, while the heavier the flow on the Abisinterface. Usually, it is recommended to be 6 ~ 10. If theAbis signaling flow load is heavy, the INTAVE value can beappropriately increased.

4.7 Interference Band Edge (LIMITn)

4.7.1 DefinitionAccording to GSM 05.08, the BTS must measure the uplinkinterference level of all idle channels, to provide thebasis for management and allocation of radio resources. Inaddition, the BTS must analyze the measurement results anddivide the interference levels into five grades to bereported to the BSC. When the MSC inquires, the BSCreports such information to the MSC. The division of thefive interference grades (interference band) can be set bythe operator on the man-machine interface. The LIMITnparameter determines the edge for dividing the fiveinterference bands.

4.7.2 FormatThis parameter is a decimal number, within the range of 0~ 62, with the meaning shown in Table 4.7 -8:

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Table 4.7-8 Interference Band

0 <-110dBm1 -110dBm ~ -109dBm-110 dBm ~ -109 dBm2 -109dBm ~ -108dBm-109 dBm ~ -108 dBm... ...61 -50dBm ~ -49dBm-50 dBm ~ -49 dBm62 -49dBm ~ -48dBm-49 dBm ~ -48 dBm

Default Value:

LIMIT1: 4; LIMIT2: 8; LIMIT3: 15; LIMIT4: 25

4.7.3 Setting and InfluenceThe division of the interference band should be conduciveto the description of the interference in the system.Usually, you are recommended to accept the systemdefaults. Generally, the idle channels have a smallinterference level, so the values of the LIMIT1 ~ 4 shouldbe small. When the obvious large interference occurs inthe system, you can appropriately increase the LIMIT1 ~ 4to learn exactly the value of the interference.

4.7.4 PrecautionsWhen you are setting them, you must pay attention to therelationships among LIMIT1 ~ LIMIT4, ensuring:

LIMIT1 ≤ LIMIT2 ≤ LIMIT3 ≤ LIMIT4

4.8 New Cause Indication (NECI)

4.8.1 DefinitionAccording to the GSM specification, the traffic channelsin the GSM system include full-rate and half-ratechannels. The common GSM systems all support full-ratechannels, while whether the network support half-rateservices is determined by the network operation

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department. The NECI parameter is used to notify the MS ifthe area supports the half-rate services.

4.8.2 Format

The NECI is a decimal number, within the range of 0 ~ 1,with the meaning described as below:

1. When the NECI is 0, it means that the cell does notsupport the access of half-rate services.

2. When the NECI is 1, it means that the cell supportsthe access of half-rate services.


4.8.3 Setting and InfluenceBecause the GSM network of China Mobile currently does notoffer half-rate services, the NECI should be set to 0.

4.9 Call Reestablishment Permission (RE)

4.9.1 DefinitionIn the case of call drop due to radio link failureresulting from abrupt interference or blind areas causedby high buildings, the MS can initiate the cellreestablishment process to recover the call, but thenetwork has the right to determine whether to allow suchcall reestablishment.

4.9.2 Format0 means that the cell allows call reestablishment and 1means that the cell does not allow call reestablishment.

4.9.3 Setting and InfluenceIn a certain environment, a MS will experience a call dropwhen it passes a blind spot. If call reestablishment is

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allowed, the average call drop ratio can be reduced.However, the call reestablishment process takes a longtime, and most subscribers have hanged up before suchreestablishment is completed. Therefore, reestablishmentdoes not achieve its purpose, while many radio resourcesare wasted. Therefore, you are recommended to disable callreestablishment on the network except for a few particularcells.

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GBC_004_E1_0 Radio Parameters Course Objectives: Contents

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Transcript of GBC_004_E1_0 Radio Parameters Course Objectives: Contents